A commercially available filter cigarette consists of a cylindrical, round or oval, tobacco rod, which is wrapped by a cigarette paper, a likewise shaped filter plug, which is surrounded by a filter wrapper paper, and also a tipping paper, which is usually adhered to the entire filter wrapper paper and to a part of the cigarette paper wrapping the tobacco rod and hence connects the filter plug to the tobacco rod.
The filter plug itself can consist of different materials, often cellulose acetate fibers are used, partly in combination with particles of activated carbon. The filter wrapping paper wrapping the filter plug is usually adhered to the surface of the filter plug along one or more narrow band-shaped areas, which usually extends or extend respectively along a direction parallel to the axis of symmetry of the filter plug. The filter wrapper paper is normally also adhered to itself along a narrow seam to prevent the filter plug from bursting open. For that purpose, a large number of different adhesives are used in the prior art, although polyvinyl acetate or hot-melt adhesives are often utilized.
Typical filter wrapper papers in the range of comparatively low and medium air permeability are composed of wood pulp, wherein a mixture of long or short fibers, depending on the desired paper properties, is used. Furthermore, these papers typically contain mineral fillers, for example calcium carbonate, kaolin, talcum, titanium dioxide or other mineral fillers and mixtures thereof Additionally or alternatively, other additives can be provided to achieve special properties, for example wet-strength additives.
Such filter wrapper papers are produced on paper machines, for example on Fourdrinier wire machines.
The cellulose fibers used for paper production are typically differentiated into long and short fibers, wherein the long fibers are typically cellulose fibers obtained from coniferous wood, such as spruce or pine, with a length of more than 2 mm, whereas short fibers are obtained from deciduous wood such as birch, beech or eucalyptus, typically having a length of less than 2 mm, often about 1 mm.
In a first step of paper production, the pulp is suspended in water and then refined in a beating machine or what is known as a refiner. It is common for short and long fibers to be refined separately. The intensity with which the pulp has been refined is determined by measurement of the refining degree, for example according to ISO 5267 (“Pulps. Determination of drainability—Part 1: Schopper-Riegler method”). The result of this measurement is given in Schopper-Riegler degrees (° SR). Typically, the long-fiber pulp for use in filter wrapper papers is refined to a degree of 50-70° SR.
Short-fiber pulp is mostly refined considerably less severely and reaches a refining degree of 15° SR to 40° SR. The refining of short-fiber pulp can also be omitted completely.
After adding fillers, for example calcium carbonate, kaolin, talcum, titanium dioxide or other mineral fillers or mixtures thereof, the fiber filler suspension flows from the headbox of the paper machine to the wire and can be dewatered there by various means, for example by gravity or vacuum. After, the moist fiber web can be passed through the press section, where it is dried by mechanical pressure against a drying felt. Finally, the fiber web can pass through the drying section, where it is dried by contact with cylinders, which for example are steam-heated. Subsequently the finished paper can be rolled up. It is possible to perform further processing steps on the paper machine, for example sizing in a size or film press, the application of watermarks, embossing, impregnation, etc.
The finished filter wrapper paper is then normally present in form of a reel, with a width corresponding to the width of the paper machine. This reel is then generally cut into narrower reels, or what are known as bobbins, the width of which results from the circumference of the filter plugs and the desired width of the adhesive seam. A typical bobbin is about 5000 to 6000 m long and has a width of 25 to 27 mm. Significant deviations in length and width of the bobbin are possible to adapt to the wide spectrum of commercially available cigarette filters. Moreover it is common for the width of a bobbin to be about an integer multiple of the width necessary for the production of one filter plug, since filter production machines can readily produce more, typically two, filter rods in parallel simultaneously.
In some filter cigarettes, one or more capsules are introduced in the filter plug and can be destroyed by mechanical pressure. These capsules contain a fluid, mostly an oil with aromatic substances, for example menthol. Hence the smoker has the possibility, through pressure on the filter plug, for example applied by the fingers, to destroy this capsule/these capsules and to thereby release the aromatic substances. The released aromatic substances then flavor the smoke flowing through the filter plug and out of the mouth end of the cigarette, so that the smoker can perceive the aromatic substances. Thus, the smoker can control the taste impression of the cigarette by destroying the capsules. Such a filter cigarette is, for example, described in U.S. 2008/142028, which is incorporated herein by reference in its entirety.
The liquid leaking out of the destroyed capsules has the tendency to penetrate through the filter wrapper paper and likewise through the tipping paper however, so that spots become visible on the outer surface of the cigarette. These spots are perceptible for the smoker and compromise the visual appearance of the cigarette.
Such spots can be avoided if the filter wrapper paper forms a certain barrier against oil. The ability of a paper to form a barrier against oil is described hereinafter as “oil resistance” and can be measured by a test common in the paper and paper-processing industry according to Tappi T559 cm-02 “Grease Resistance Test for Paper and Paperboard”. In this test, drops of 12 different test liquids sorted in ascending order according to their wetting ability are applied to the paper and it is then determined which of the liquids penetrates to the other side of the paper. The result of the test is the so-called KIT level, which describes for which test liquid the penetration to the other paper side occurred first. Hence it is described by a number between 1 and 12, wherein higher values correspond to a higher barrier effect against oil. In case the first test liquid penetrates through the paper, the result is denoted as “<1”. For a filter wrapper paper for the application as described above, a KIT level of about 5 has proven to be sufficient to avoid the forming of spots on the cigarette.
One possibility to provide the paper with such a barrier function against oil or with “oil resistance” consists in coating the filter wrapper paper with fluorinated hydrocarbons, which provide the paper with oil-repellent properties. Such fluorinated hydrocarbons are commonly used for example in food packaging made out of paper, but are not allowed for use in cigarettes in many countries. Additionally, this coating can complicate the adherence of the filter wrapper paper.
Besides fluorinated hydrocarbons, it has also been suggested to use specially modified starch products, specifically starches substituted with octenyl succinate, for impregnation of papers for food packaging, see WO 2008/100688. However, these starches have the disadvantage that to achieve the desired effect, they have to be applied to the paper in a comparatively large amount. A sufficient effect could only be achieved with an application of an amount of more than about 80 kg of this starch product per ton of paper.
If the proposed method were applied to a filter wrapper paper, this ratio would correspond to an application of typically more than 2 g/m2. This would increase not only the material costs, but also the energy demand for drying in an unfavorable manner.
Also in CA 2467601, the application of starch products to achieve oil resistance is described. There, it is suggested to use a composition consisting of a modified starch, an agent to increase the mechanical flexibility, for example glycol, and an agent for the adjustment of the rheological behavior. Although the mechanical flexibility of the coating can be improved, it is necessary according to that patent specification to apply more than 75 kg of this composition per ton of paper in order to ensure sufficient oil resistance. Hence also here the material consumption and the related costs for material and energy for drying of the paper are comparatively high. The effect could also only be demonstrated for papers with a basis weight of more than 37 g/m2, which corresponds to an application of at least 2.78 g/m2. It is in no way obvious that the effect described in the above patent specification can be readily transferred to filter wrapper papers with a significantly lower basis weight. Moreover the use of glycols in papers for cigarettes is not allowed in some countries.
In the case of filter wrapper papers, which are generally substantially lighter and thinner than food packaging papers, proportionally higher application amounts of these starch products are needed based on the paper mass, because the papers can only provide less resistance to the oil due to their low basis weight and low thickness, and because, due to the low basis weight, the application per weight unit of the filter wrapper paper occurs over a comparatively larger area.
Besides additional costs, the application of large amounts of starch products brings about also further disadvantages. For example, papers which are coated intensively with starch tend to dust, which increases the number of cleaning cycles on processing machines and reduces their productivity.